1. Field of the Invention
This invention relates to machines for packaging articles such as cans, bottles, cartons and the like in each of a series of trays. The invention relates particularly to packaging machines that are operative, in sequence, to draw a film sheet from a roll of the film over the articles in a tray, to cause the sheet to adhere to at least one pair of opposite tray walls, and to hold the articles in the tray.
2. Description of the Prior Art
Machines for packaging articles of various kinds in a series of trays that operate in accordance with the sequence above described are known in the prior art. Such a packaging machine is disclosed in my prior U.S. Pat. No. 3,890,763 issued on June 24, 1975 and incorporated herein by reference. The packaging machine there illustrated and described, a high speed WRAPCAP machine made by Huntington Industries, Bethayres, Pa., includes a conveyor for moving a series of rectangular corrugated paperboard trays along a predetermined path. Arranged in succession along said predetermined path are a first glue station, a turning station, a second glue station, a film disposing station, and a compression station. At the first glue station glue applicators, which may be spray guns, are provided on opposite sides of the path for applying a stripe of adhesive on the outside walls (the long walls), of each tray as the latter moves past the glue applicators. Rotatable arms are provided at the turning station for rotating the tray through a right angle so that the trays then advance with the adhesion stripe on the leading and trailing walls. Additional glue applicators are provided on said opposite sides of said predetermined path at the second glue station for applying a stripe of adhesive on the outside of the other opposite walls (the short walls), of each tray. At the film disposing station a supply of film, for example of polyvinyl chloride, polypropylene or polyethylene, is provided. As the tray moves through the film disposing station, the sheet film is drawn tautly over the top of the tray. The sheet film is pulled from a constant tension unwind mechanism by a preceding tray which then is in the compression station and is being moved along by a flight bar. A succeeding flight bar pulls the sheet tautly down over the tops of the articles in the first mentioned tray and firmly against the applied adhesive on its trailing wall to form a tight band. As a result, the film sheet makes firm contact with the adhesive on the walls of the tray to form a tight bond. Cutting blades are provided in cooperative relation with the flight bars for piercing and separating the sheet between trays. After the sheet has been cut, the tray is released and is discharged from the compression station, being given a parting push by the trailing flight bar. The tray then moves on a downwardly inclined conveyor to an interconnecting conveyor which leads to a shrink tunnel. In the shrink tunnel, the heat shrinking of the sheet brings its unbonded side portions into contact with the second pair of adhesive strips to form a bond. Additionally, spring-loaded rollers are provided at opposite sides of the exit from the shrink tunnel to flatten out rough ears formed by the side portions of the sheet and to press the side portions of the sheet against the adhesive to form a better and more attractive bond. As stated in said prior patent, even when the second pair of adhesive strips is not applied to the tray walls the pressure of the rollers causes the hot ends of the sheet to adhere to the walls.
Trays packaged by the packaging machine of my aforementioned patent have a number of advantages over the conventional rectangular corrugated paperboard case, including weight savings, lower costs, locking of the articles in the tray to prevent relative movement of the articles, transparency of the covering film sheet so that labels and other information provided on the tray may be seen, absence of film sheet from the bottom of the tray, and easy removal of the articles from the tray by slitting the film.
However, the glue tends to obscure labels or other information which it overlies on the walls of the trays. The need for adhesive and adhesive apparatus adds to the cost of packaging. Also, the need for a turning station, for turning the trays through a right angle so that the adhesive striped walls are leading and trailing, adds to the complexity and size of the packaging machine.